Foil seal



Jan. 14, 1969 L. p. LUDWIG 3,421,768

FOIL SEAL Filed April 20, 1966 INVENTOR. LAWRENCE P LUDW/G F126 BY QA/hsv wwzil United States Patent 12 Claims ABSTRACT OF THE DISCLOSURE Acircular foil disc mounted on a rotating shaft in close proximity with aspirally grooved plate forms a seal. The fluid to be sealed enters aradial gap between the disc and plate, and the movement of the rotatingdisc relative to the plate creates a pumping action which preventsleakage.

The invention described herein was made by an employee of the UnitedStates and may be manufactured and used by or for the Government forgovernmental purposes without the payment of any royalties thereon ortherefor.

The present invention relates to seals and relates more particularly tostructures for effecting a seal between relatively moving parts.

Prior devices have not been entirely successful for effecting sealsbetween relatively moving parts because of wear, misalignment anddifferences in thermal expansion characteristics of the sealing elementssuch that a tightly closed fluid sealing fit cannot be continuouslyassured between the relatively moving parts.

It has been a particular problem to retain oil around a rotating shaftwhich projects from the interior of an oil containing machine housing.In the past, centrifugal Slingers have been mounted on the rotatingshaft for moving the oil back into the housing during operation of themachine, thereby preventing passage of oil around the rotating shaft.Other sealing devices utilize a contact seal wherein a seal iscontinuously in sliding contact with the shaft. These and other sealshave not been entirely successful in preventing axial movement of thefluid past the seal.

The present invention provides a seal structure wherein the relativemovement of the parts is used to effect a seal. The present sealstructure provides an absolute seal against through flow of fluids pastthe seal.

In a preferred form of the present seal, the sealing function isperformed between a closely spaced flexible sealing element disposed inclosely spaced relation to a grooved or recessed relatively rigidsealing element. The sealing elements are disposed so that any axialflow of the fluid to be sealed must pass through the space between thesealing elements. The sealing elements are further arranged to moverelatively. The relative movement of the flexible sealing element overthe grooved or recessed sealing element increases the pressure of thefluid in the grooves or recesses to at least the fluid source pressureto effect at least a static condition. In one embodiment the fluid to besealed is forceably moved in the grooves. In a preferred form of thisembodiment the grooves are arranged or directed toward the source of thefluid to be sealed so that the fluid is effectively pumped back to thesource.

In a specific embodiment, one of the sealing elements is carried by ahousing and the other sealing element is fixed to a shaft for rotationrelative to the housing. The space between the sealing elements and inthe grooves in the rigid sealing element communicate with a fluidcontaining chamber in the housing. Portions of the grooves furthest fromthe chamber lead the remaining portions of the grooves relative to themovement of the flexible sealing elements so that fluid is forced backinto the chamber.

An object of the present invention is to provide a new and improved sealbetween relatively moving parts.

Another object of the present invention is to provide a new and improvedseal between relatively moving parts wherein the relative movementbetween the parts creates an area of high pressure which prevents fluidflow through the seal.

Still another object of the present invention is to provide a new andimproved seal between relatively moving parts which is simple inconstruction, economical of manufacture and is substantially wear free.

Other objects and a fuller understanding of the invention may be had byreferring to the following description and claims taken in conjunctionwith the accompanying drawing in which:

FIGURE 1 is a cross-sectional view, taken along a longitudinal plane, ofa machine having a through shaft and utilizing the seal structure of thepresent invention to seal against an axial flow of fluid out of themachine at the shaft;

FIGURE 2 is a cross-sectional view, taken along a lateral planeindicated by the lines 22 in FIGURE 1, showing the face of a recessedsealing plate used in the seal structure of FIGURE 1;

FIGURE 3 is a cross-sectional view, similar to FIG- URE 2, showing analternate sealing plate;

FIGURE 4 is a fragmentary, cross-sectional View, taken along alongitudinal plane, showing an alternate embodiment of the sealstructure of the present invention;

FIGURE 5 is a fragmentary, cross-sectional view, similar to FIGURE 4, ofstill another alternate embodiment of the seal structure of the presentinvention; and,

FIGURE 6 is a fragmentary view, taken along a lateral plane indicated bythe line 66 in FIGURE 5 of the sealing structure of FIGURE 5.

Referring now to the drawings, a preferred form of the seal of thepresent invention is designated generally by the reference character 11in FIGURES 1, 2. The seal 11 is adapted to provide a seal between ashaft 12 rotatably mounted in a machine housing 13 as by the bearing 14.The machine housing 13 is a part of machinery having a protruding,rotating shaft such as a motor, a workpiece working machine or the like.

A flexible seal disc 21 is mounted on the shaft 12 and has a centralaperture 22 sized to receive the shaft 12. The disc 21 extends radiallyfrom the shaft 12 to an outer peripheral edge 23 which describes acircle concentric with the aperture 22. The disc 21 is fixed to theshaft 12 to rotate therewith by central portions of the disc 21 whichare clamped between cylindrical clamping members 25, 26. The clampingmember 25 abuts against a bearing half-race 27 of the bearing 14 whichprevents movement of the clamping member 25 toward the interior of themachine. The clamping member 26 is threaded on the shaft 12 to clamp thedisc central portions tightly against the clamping member 25. A setscrew 28 fixes the clamping member 26 to the shaft 13 and prevents aloosening movement of the clamping member 26 to retain the disc 21rigidly fixed to the shaft 13.

The disc 21 is a flexible member made of a metal foil, preferably No.304 stainless steel. As an example, in the machine shown having a shaftapproximately .438 inch in diameter, a preferred stainless steel disc is3.75 inches in diameter and is .005 inch thick.

A spirally grooved rigid seal plate 31 is carried by the housing 13 andis fixed to it by conventional fasteners 32. The fasteners extendthrough apertures in outer mounting flange portions of the seal plateand are threaded into tapped bores in the housing 13. In the seal 11shown, the seal plate 31 is made preferably of a resinous, syntheticplastic material, for example, Lucite. The plate 31 has a centralaperture 33 which axially receives the shaft 12. A raised and groovedface surface 35 extends radially, generally parallel to the disc 21 andis spaced from the disc 21.

Referring to FIGURE 2 the face of the seal plate 31 includes a pluralityof spiral grooves or recesses 3740 which start at 90, angularly spacedpositions around the central aperture 33. The spiral grooves 37-40spiral away and around the central aperture for 1 /2 turns (540) from aone inch inner diameter to a four inch outer diameter in the preferredseal plate shown. The spiral grooves or recesses 3740 in the plate shownas an example herein are preferably from .007 to .011 inch deep and .12inch wide. The grooves or recesses are separated by lands .08 inch wide.

An inner annular surface 43 of the machine housing 13 extends radiallyfrom an inner surface 44 which defines a shaft receiving bore throughthe machine housing, to an outer cylindrical surface 45 beyond the outerperipheral edge 23 of the seal disc 21. A radial surface 46 extendsfurther radially outward from the surface 45 and a cylindrical surface47 extends from the outer perimeter of the surface 46 to an annularsurface 48 to which the seal plate 31 is fixed by the fasteners 32.

The machine surfaces 43, 45 and the face surface 35 of the seal platedefine a fluid chamber 50 into which the seal disc 21 extends in closeproximity to the face surface 35. The surfaces 46, 47 define an annularfluid receiving pocket around the periphery of the seal disc 21.

When no forces are acting on the disc 21, as when the shaft 12 isstationary, the disc 21 extends in a radial plane slightly furtherspaced from the face surface of the seal plate 31 than is shown in thedrawings of FIG- URE 1. In the size of seal 11 shown herein as anexample, the radially extending space or gap between the disc 21 and thesurface of the seal plate is on the order of 0.005 inch when the fluidto be sealed is a liquid and on the order of 0.005 inch when the fluidto be sealed is a gas.

A lubricating fluid or the like which is placed in the chamber 50 entersthe narrow radially extending space or gap between the foil disc 21 andthe spirally grooved seal plate 31. When the machine is placed inoperation and the shaft 13 is rotating, the fluid to be sealed,partially or completely fills the radially extending space between theseal disc and the seal plate. The fluid is prevented from leakingaxially past the seal by a pumping action provided by the flexible foildisc moving the fluid in the spirally arranged grooves of the sealplate.

Where the fluid or other material to be sealed at the higher pressurefirst enters the seal around the outer peripheral edge of the disc 21 inthe arrangement shown with the shaft 13 rotating in a clockwisedirection as shown by arrow 36 an outwardly pumping arrangement of thegrooves is utilized. The foil disc 21 wiping across the groovescontinuously forces the fluid to the outer periphery of the seal plate31 and continuously pumps the fluid away from the central aperture ofthe seal plate thereby preventing its egress past the shaft seal 11. Thepumping action may be described as outwardly pumping for the arrangementshown wherein the fluid under pressure is on the chamber or right sideof the flexible disc 21 as shown in the drawing.

Should the arrangement be reversed wherein the fluid to be sealed at thehigher pressure enters the seal through the :aperture 33 in the sealplate 31 to the inner peripheral edge of the radially extending spacebetween the disc 21 and the plate 31, then an inwardly pumpingarrangement is used to seal against axial movement of the fluid past thedisc 21. The inwardly pumping arrangement is provided by reversing thedirection of rotation of the the shaft 13 oppositely as shown by thearrow 36 or by reversing the direction of spiral of the grooves 37-40 inthe plate 31. In an inwardly pumping arrangement for the direction ofshaft rotation shown by the arrow 36 the grooves are arranged to spiralaway from the central aperture of the plate in a counterclockwisedirection rather than in a clockwise direction as shown. Movement of theflexible disc 21 over the fluid in the grooves forces the fluid towardthe center aperture and prevents it from flowing into the chamber 50. Inboth arrangements, the portions of the grooves closest to the fluidsource lag behind the portions of the grooves furthest from the fluidsource relative to the movement of the flexible disc 21.

Where the fluid or material to be sealed is in a gaseous or vapor state,an alternate seal plate 55 having a grooved herringbone arrangementshown in FIGURE 3 is utilized.

In the herringbone arrangement, an inner annular portion of the raisedface surface of the seal plate 55 contains outwardly pumping grooves 56and an outer annular portion contains inwardly pumping grooves 57. Theoutwardly pumping grooves 56 extend from the inner peripheral edge ofthe seal plate 55 to generally half way between the inner and outerperipheral edges of the seal plate. The inwardly pumping grooves 57extend from the outer ends of the outwardly pumping grooves to the outerperipheral edge of the seal plate 55.

With the seal plate 55 in the seal assembly of FIG- URE 1, a portion ofthe vapor between the foil disc 21 and the seal plate 31 is condensed onthe face surface of the seal plate 55. As the foil disc rotatescounterclockwise as seen in FIGURE 3 relative to the seal plate surface,the liquid resulting from the condensed vapor is pumped toward theintersection of the outwardly and inwardly pumping grooves 56, 57 andremains trapped there because the contra pumping action of the grooves.This results in an annular ring or slug of the liquid being trappedwhere the inwardly and outwardly pumping grooves meet as shown by brokenlines 59. The slug of liquid thusly trapped seals against the flow ofgases or vapors through the gap between the flexible disc 21 and theseal plate 55.

In its preferred form, as shown in FIGURES 1, 2, the present seal ispressure compensating in that an increase in fluid pressure in thechamber 50 moves the foil disc closer to the grooved seal plate 31 toincrease the pumping action of the mechanism thereby adjusting for thepressure increase. Axial growth or other relative movement of the shaft13 relative to the housing 12 is accommodated by the present mechanismthrough the flexibility of the foil disc 21. The foil disc 21 allowsrelative movement in either axial direction. Relative radial growth ofthe flexible disc 21 and the seal plate 31 is accommodated in thepresent mechanism by reason of their parallel, radially extendingarrangement. Radial movement or growth either of the disc 21 or theplate 31 does not affect the pumping action provided by them.

Referring to FIGURE 4, another embodiment of the foil seal of thepresent invention is designated generally by the reference character 71,The foil seal 71 utilizes centrifugal force to actuate a foil disc 72toward spiral grooves 73 and establishes an inherent increased pumpingeffort as the speed of rotation of the foil disc 72 increases,

In this arrangement, the foil disc 72 extends radially from a rotatingmember 74, which, for example, is the rotor of a compressor. The foildisc 72 extends behind the face surface of a rigid, annular seal plate75 fixed to a stationary member 76, for example, a stator. The sealplate 75 has spiral grooves 73 similar to the grooves in the seal plate31 described above, except arranged in an inwardly pumping arrangement.The foil disc 72 is placed ahead of the seal plate 75 by bending thefoil forwardly whereupon it assumes the angle shown in phantom at 72'which is its position when stationary relative to the seal plate 75. Asthe rotor 74 commences rotating, a pumping action is provided by theinteraction of the innermost interface portions of the disc and thegrooved seal plate surface only. As the speed of rotation increases thedisc 72 tends to extend further radially outward by reason ofcentrifugal force. Its free edge at its perimeter moves from itsdiverging position relative to the seal plate to a position closer andmore parallel to the grooved seal plate surface increasing the interfacearea in close fluid pumping relation. Thus, as the centrifugal forcesincrease from increased speed of rotation, the foil disc 72 is actuatedtoward the spiral grooves 73 and establishes an inherent increasedpumping effort.

Referring to FIGURES 5 and 6, an alternate seal is designated generallyby the reference character 81. In this arrangement, a rigid, annularseal plate 82 includes a plurality of circumferentially spaced andrecessed chambers 83 in the face of the seal plate 82. An opening ororifice 86 through the seal plate 82 substantially in the center of eachof the recessed chambers 83 provides communication through the sealplate to the high pressure side of the seal plate 82. A flexible foildisc 87 extends radially from the rotor 74 on the fluid side of the sealplate 82 and in superposed relation with the rigid seal plate.

The material to be sealed, such as a gas, in one stage of the apparatus,for example a compressor, is at the highest pressure designated P and onthe right side of the seal as shown in FIGURE 5. A lower pressure P maybe outside the compressor such that it is the ambient pressure or it maybe the pressure in the next stage of the compressor. The gas to besealed enters the seal between the flexible disc 87 and the rigid sealplate 82 along an inner peripheral edge of the seal space or gap. Thereis some pressure drop through the orifices 86 to the chambers 83. As theangular speed of the rotor 74 increases, the foil disc 87 tends to takethe more parallel position shown by the solid line 87 instead of thediverging position shown by the broken line 87' by reason of centrifugalforce. This increases the pressure P in the recessed chamber 83 untilthere is a pressure balance between the pressure P in the chambers 83and the pressure P of the gas to be sealed. Since this pressure in therecessed chamber 83 approaches the pressure sealed, gas flow through theseal is restricted.

In all of the above seals, the sealing function is provided by closeclearance between the flexible foil and the grooved solid surface of theseal plate and the relative motion between the two surfaces. Contactbetween the surfaces is prevented by a balance between the forcespushing the foil towards the face of the seal plate and the forces inthe fluid between the foil and the seal plate. In the seal embodiment 11shown in FIGURES 1-4, the self-acting or hydrodynamic forces induced inthe fluid in the gap between the interface surfaces of the foil and theface plate are in balance with the hydraulic and/or pneumatic forces,depending upon the nature of the fluid to be sealed, pushing the foiltoward the seal plate, any mechanical force which may tend to be appliedas by the internal resiliency of the flexible foil seal when arranged inan off-set arrangement, and in balance with centrifugal forces as areapplied in the arrangement of FIGURE 4. In the arrangement of FIGURES 5and 6, the hydrostatic or externally pressurized forces are maintainedin balance with the centrifugal forces applied, the mechanical forcessuch as by the tendency of the foil to straighten, and hydraulic and/orpneumatic forces as determined by the nature of the fluid or fluidsaround the seal.

In all these seal embodiments, the metallic foil seal provides excellentgap control by establishing and maintaining the gap at a minimum valuethereby increasing sealing effectiveness. This effective sealing ismaintained while simultaneously allowing free axial or radial growth orrelative movement. In addition, the metallic foil seal is able toconform to any irregularities in the face surface of the seal plate,e.g., waviness, and to accommodate runout of the seal plate facesurface.

Although the invention has been described in its preferred form with acertain degree of particularity, it is understood that the presentdisclosure of the preferred form has been made only by way of exampleand that numerous changes in the details of construction and thecombination and arrangement of parts may be resorted to withoutdeparting from the spirit and the scope of the invention as hereinafterclaimed.

What is claimed is:

1. A fluid seal device for preventing a flo-w of fluid through amechanism comprising:

(a) a thin, flexible sealing element;

(b) a relatively rigid sealing plate having a groove in a face surfaceof the plate;

(c) said flexible sealing element being disposed in confronting, closelyspaced relation to the face surface of the sealing plate;

(d) said sealing element and said sealing plate in their confronting,closely spaced relation being disposed so that fluid flow must bethrough the space between them;

(e) means for causing relative movement between said sealing element andsaid sealing plate whereby the sealing element in moving relative to thesealing plate increases the pressure in the sealing space between thesealingelement and the grooved sealing plate to at least the pressure ofthe fluid to be sealed so as to prevent through fluid flow; and

(f) each of said grooves having a portion closest to the fluid laggingbehind the portions furthest from said fluid as taken in relation to therelatively moving flexible sealing element so that fluid entering saidsealing space is moved back towards said fluid.

2. A device as claimed in claim 1 wherein said groove is on a lowpressure side of the sealing plate and in communication with a highpressure side of the plate whereby the pressure in the sealing spacebetween the sealing element and the sealing plate does not exceed thehigh pressure.

3. The device of claim 1 wherein said sealing element rotates relativeto the sealing plate and the groove is arranged in a spiral around thecenter of rotation.

4. A fluid seal comprising:

(a) a housing member defining a chamber containing fluid to be sealedtherein;

(b) a rotatable shaft member extending through the chamber and beingrotatably journaled in said housing member;

(c) first and second sealing elements being closely spaced and extendingaround said shaft;

((1) one of said elements being fixed to said housing, the other of saidsealing elements being fixed to said shaft so as to be rotatable withthe shaft and relative to said one sealing element;

(e) one of said sealing elements being flexible and the other of saidsealing elements having at least one groove facing the flexible sealingelement;

(f) said sealing elements being orientated so that the space betweenthem communicates with said chamher; and,

(g) each such groove having their portions closest to said chamberlagging behind their portions furthest from said chamber as taken inrelation to the relatively moving flexible sealing element so that fluidentering said space from said chamber is moved back toward said chamber.

5. The seal of claim 4 wherein the flexible sealing element is fixed tosaid shaft.

6. The apparatus of claim 4 wherein interface surfaces of the sealingelements extend in generally radial directions relative to the axis ofrotation of said shaft.

7. The apparatus of claim 5 wherein each such groove extends spirallytoward the fluid containing chamber.

8. The sealing device of claim 4 wherein a plurality of fluid conveyinggrooves are provided and extend from near the center of said platetoward the outer periphery 7 8 of the plate at non-radian anglesrelative to the center of 10. The fluid seal of claim 9 wherein saiddisc element rotation. is a thin metallic foil disc.

9. A fluid seal comprising: 11. The fluid seal of claim 10 wherein saidmetallic (a) housing means defining a chamber containing the foil discis on the order of 0.005 inch in thickness.

fluid to be sealed therein; 5 12. The fluid seal of claim 9 wherein thespace between (b) said housing means having an outlet opening comthedisc and the seal plate is on the order of 0.005 inch.

municating with the chamber; (0) an annular seal plate means carried bysaid hous- References Cited ing means and extending around said opening,said UNITED STATES PATENTS seal plate means having grooves around saidopening; 10

(d) a flexible disc element being disposed in closely 3 f spaced,confronting relation to the seal plate means; 3093382 1/1963 232 X (e)rotatable means connected to said flexible dlsc 3,109,658 11/1963Barrett et a1 277 96X element for causing angular rotation of the discelement relative to the sealing plate means in close 1 3188097 6/1965cott 277 95 X proximity thereto; and FOREIGN PATENTS (f) the grooves insaid seal plate means extending out- 735,250 8/1955 Great Britain wardlyrelative to a center of rotation of the flexible disc element and at anangle relative to a radius from SAMUEL ROTHBERG, Primary Examine]; theaxis of rotation such that the portions of the 20 grooves furthest fromthe center of rotation lead the US. Cl. X.R. portions of the groovecloses to the center of rotation 27774, 95

relative to the moving disc element.

